HOW TO: Bench-synch your carbs

thanks a lot.... Also, the mixture screws still have the caps on all of them except for #3. Do I need to drill them out to adjust them or could I be alright without adjusting? I figure they've been as is since 1983 and I'm not changing the exhaust or going with pod air filters.....sooooooo....... ????

 

you wont be able to tune the motor unless you can get to the pilot mixture screws & I would be at least fitting new 'O' rings.

 

New O rings where? Sorry if that's a stupid question.

 

On the pilot mixture screws, idealy change the screws, springs, washsers & '0' rings, complete.

 

Does all of that come in a rebuild kit? I need to just suck it up and order one.

 

Yes.
Funny you should ask!!!

The supply the New O-ring ... AND, And, and ... 4 New Blind Plugs.

You are going to HAVE to Drill-out the Original ones.
You start a small hole in the middle of the Plug
Drill-out just enough material to get a self-tapping screw some bite.

Start the screw into the drilled hole
Grab the screw with Vice Grips
Knock the Vice-grips pulling the Plug out of its hole.

CAUTION
-and-
WARNING

You MUST exercise caution to make the drilled hole deep enough for a screw to take hold ... OR ... Allow the Drill to go completely through the Plug ... WITHOUT ALLOWING the Drill to come into contact with the HEAD of the PILOT MIXTURE SCREW which is located VERY CLOSE to the Plug.

The Drill will DAMAGE the Top of the Screw and make Extraction and Tuning very difficult.

 

Awesome Rick. Thanks for the info. I wanted to call you today, but didn't get around to the bike. I got caught up with yard work and my afternoon nap took the place of working on the bike Now I work 12 hour days the next two days and will be doing family stuff all weekend, so might not touch the bike until next Wednesday. I guess that's perfect, because then I could get all the stuff mailed that I'm going to need. I emailed Chacal, but he just gave me a list a mile long of parts. There were just too many options. I just want to say..... please give me a rebuild kit and someone that knows better than I do what I'll need will put it together in a nice pretty package and send it my way

 

Carb Rebuilding FAQ:


Question #2: What Parts Will I Need?:

The parts you'll need depends on what is there, what is missing, what is worn out, what gets broken or damaged during the dis-assembly process, etc., but the "basic items" needed for the rebuild process (besides any special tools and tuning equipment) is as follows:

- throttle shaft seals (you'll have to split the carbs from the rack to replace these).

- fuel supply tube o-rings (you'll have to split the carbs from the rack to replace these) on the models that use them (some Mikuni carbs do not use these).

- float valve needle and seat rebuild kit (seat, needle, clip, seat washer. The float valve seat filter screens are also available separately). Mikuni owners will also want to replace the float valve seat o-rings.

- float bowl gaskets.

- idle mixture washers & o-rings for sure, and the idle mixture screw springs and screws if they are damaged.

- jets, if damaged or incorrectly sized.

- carb bowl fuel drain screws, if damaged.

- new replacement carb hardware (screws, etc.)---now is the time to upgrade to stainless steel and/or allen-head fasteners if so desired!

 

does anyone have a pic of the idle mixture washers and o-rings torn down? I mean....to show where they go and skool me on what the hell I need to do if I want to replace them.

I got a rebuild kit, but it only contained the float valve seat, clip, washer, and float bowl gaskets. I didn't even bother replacing them, because my stuff looked good.

I don't want to split the carbs from the rack, so I don't want to replace the other stuff above unless I absolutely have to.

I might pick up a jet kit to replace all the jets though.

For now I'm leaving them as is and I just bench synghed them and I'll see how it goes tomorrow when I reinstall them and try to get the bastard running. I'll most likely be back on here asking for help and parts from chacal

 

Good pix of the idle mixture/pilot circuit screws on this thread:

http://www.xjbikes.com/Forums/viewtopic/t=3690.html

 

This might help, but it goes, spring,washer, 'O' ring.

 

thanks.... that link was PERFECT! Amazing amount of detail on some insanely clean carbs. Thanks chacal

 

After performing this procedure as described, my center sync screw is still almost bottomed out. I remember reading in another thread that this should not be the case. My butterflies are adjusted and all seem pretty equal, though, so I'm at least starting off close...I think. I just don't have any experience to draw upon as far as whether or not I might need to be able to tighten that screw further once it's on the bike.

Thanks.

 

The difference between a good bench sync and a running sync should be no more than a half turn of a screw.

It does sound like something is wrong. like carb alignment or the re-installation of a butterfly not fully "square".

 

Look at the position of Gamaru's middle screw in the initial post, though. The picture between instructions #6 and #7 show that screw cranked all the way in, too.

 

I've used Gamuru's technique every time and can tell you
it works great.

Rick....thanks for the pic and advise. I can still remember
reading your carb cleaning write-up a couple of years ago
and the part about the pilot screws getting stuck and needing
drilling out gave me the chills (I was such a newbe).
Thankfully it all went well.

 

To get the details right, ... I had to take a carb apart while I was writing the piece.

Family and visitors using the computer for what-not were shocked to find carb parts all-over the computer desk-top.

 

Is this only for xj650 or can this be done on a xj750??

 

i was lost after the main post.

 

alright so this sounds like a stellar write up! Im not sure if my browser is blocking pics or are they are no longer hosted wherever they were originally hosted? All I see is an icon labeled IMG...would love to see the pics....anyways. Is this as accurate as using a manometer or the "2 bottle system"?